A. Technical Field of the Invention
The invention relates to a suction device for the formation of a tobacco rod for use in cigarette manufacture. Such a device is equipped with a suction-type rod conveyor which employs an air-permeable belt to transport tobacco shreds along a tobacco channel.
Such equipment may also have a pre-equalizer which equalizes the height of the tobacco rod being conveyed by removing part of the tobacco rod. It also may be provided with a device that compacts the tobacco rod at regular intervals and an equalizer which uniformly sets the height of the tobacco rod to a pre-specified height by removing additional tobacco from the tobacco rod.
B. Description of the Related Art
The device is part of a cigarette rod-making machine. In cigarette rod-making machines, tobacco shreds in the form of a shower of loose tobacco are aspirated by negative pressure from below onto the continuous, air-permeable belt of a suction-type rod conveyor. The formed tobacco rod is placed onto strips of wrapping material and wrapped in them. The continuous tobacco rod thus created is then cut into individual cigarettes. In order to obtain a uniform tobacco density inside the cigarettes, it is necessary to form a cigarette rod on the suction-type rod conveyor and the height of the rod must be as uniform as possible. In order to prevent the tobacco shreds from spilling out, cigarettes have a somewhat higher tobacco density at their tip. For this reason, at regular intervals, the tobacco rod being formed on the rod conveyor is compacted, for instance, by means of a rotating cam.
Pre-equalization of the height of the tobacco rod takes place prior to compacting, while the final equalization of the tobacco rod is carried out after compacting. For purposes of pre-equalization, it is a generally known to employ paddle wheels which are positioned diagonally to the direction of the tobacco rod and which remove protruding tobacco from the rod surface, pushing it to the side (EP-A 0,645,098); a cylindrical, rotating disk whose rotational plane is perpendicular to the direction of the height irregularities of the tobacco rod is also known (EP-A 0,465,414). The latter pre-equalizer makes it possible to remove excess tobacco from the tobacco rod in a relatively gentle manner, so that it can then be returned to the production process without a detrimental effect on the quality.
Difficulties arise in connection with the use of tobacco mixtures which have a high proportion of Oriental tobacco since such tobacco mixtures have considerably more ribs than are found, for example, in American tobacco blends; moreover, problems are also encountered when tobacco mixtures having very long shreds are used, as is increasingly the case due to improved tobacco preparation techniques and also when tobacco shreds having a larger cut width are used, for instance, up to the 3.5 mm typically found in smoking products instead of the commonly employed cut width of, for example, 0.85 mm. With such tobacco mixtures, there is a risk that additional tobacco shreds will be pulled out of the tobacco rod, so that, following the pre-equalization procedure, there will be a hole or a thin spot in the tobacco rod at a site that was previously occupied by tobacco.
For purposes of the final equalization, devices are known which have two overlapping circular blades (EP-A 0,137,604). One of these circular blades can also have a serrated edge (U.S. Pat No. 3,413,979 and GB-C 1,024,941). The equalizer can be fitted with two retaining disks touching each other along their circumference, between which any protruding tobacco shreds are clamped, after which the protruding tobacco shreds are cut off by means of a scraper, a rotating blade, a tubular cutter (DE-A 4,202,198) or a paddle wheel (DE-A 3,407,893). The tubular cutter employed according to DE-A 4,202,198 consists of a leading edge formed by the triangular or rectangular teeth of a rotating, tubular element. The axis of the tubular element faces the direction of the tobacco rod and it is inclined downwards. The cutting edge of the tubular cutter that is active at any given moment is positioned perpendicular to the tobacco rod. These equalizers are very complex and call for a precise alignment of the individual components. They require a relatively large space. For these reasons, they have not yet been used as pre-equalizers.